Systems Investigation of Vaccine Responses in Aging and Frailty

Inclusion Criteria: * Age 21-40 or 65 and older * Ability to understand and give informed consent (surrogate consent may apply to nursing home subjects who are decisionally impaired, with verbal assent to be obtained from subject) * Plan to be in the New Haven, CT area for the next 4-6 weeks Exclusion Criteria: * Current use of medication, such as antibiotics in past two weeks. To clarify, patients taking antibiotics for the reason of a current acute infection will not be eligible. Those potential participants receiving antibiotics for prophylaxis purposes will be eligible to participate. The intention is not to create a separate group to drawn conclusions, but not to exclude these participants who are not acutely ill. * Evidence of acute infection, identified by self- report of fever or symptoms in past two weeks * Treatment for cancer in past three months. * Previous adverse reaction to influenza vaccine requiring medical attention, such as allergic response (rash, anaphylaxis) or Guillain-Barré syndrome. * Pregnant/possibly pregnant. * History of organ, bone marrow or stem cell transplant, liver cirrhosis, kidney disease requiring dialysis, HIV/AIDS, hepatitis C or active hepatitis B * Blood donation of 1 pint or more in past 2 months * Treatment with clinical trial medication * Presence of any other condition (e.g., geographical or social), actual or projected, that the investigator feels would restrict or limit the patient's participation for the duration of the study. This provision includes participants who have 50% or more missed appointments in the last three months.